The parameters used to describe the electrical conductivity of a porousmaterial can be used to describe also its thermal conductivity. Anew relationship is developed to connect the thermal conductivityof an unsaturated porous material to the thermal conductivity ofthe different phases of the composite, and two electrical parameterscalled the first and second Archie's exponents. A good agreementis obtained between the new model and thermal conductivity measurementsperformed using packs of glass beads and core samples of the Callovo-Oxfordianclay-rocks at different saturations of the water phase. We showedthat the three model parameters optimised to fit the new model againstexperimental data (namely the thermal conductivity of the solid phaseand the two Archie's exponents) are consistent with independent estimates.We also observed that the anisotropy of the effective thermal conductivityof the Callovo-Oxfordian clay-rock was mainly due to the anisotropyof the thermal conductivity of the solid phase.